Add TraceMessage for observability

[svilupp]

• Added a few new open-weights models hosted by Fireworks.ai to the registry (DBRX Instruct, Mixtral 8x22b Instruct, Qwen 72b). If you're curious about how well they work, try them!
• Added basic support for observability downstream. Created custom callback infrastructure with initialize_tracer and finalize_tracer and dedicated types are TracerMessage and TracerMessageLike. See ?TracerMessage for more information and the corresponding aigenerate docstring.

Example

wrap_schema = PT.TracerSchema(PT.OpenAISchema())
conv = aigenerate(wrap_schema, "Say hi!"; model = "gpt4t", return_all = true)
all(PT.istracermessage, conv) #true

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 81.81818% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 93.13%. Comparing base (9482d67) to head (4928cdb).

:exclamation: Current head 4928cdb differs from pull request most recent head 055819f. Consider uploading reports for the commit 055819f to get more accurate results

Files	Patch %	Lines
src/messages.jl	77.35%	12 Missing :warning:
src/templates.jl	33.33%	8 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #133 +/- ## ========================================== - Coverage 93.38% 93.13% -0.26% ========================================== Files 41 42 +1 Lines 2947 3058 +111 ========================================== + Hits 2752 2848 +96 - Misses 195 210 +15 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.